Fine-adjustment potentiometer

ABSTRACT

A fine-adjustment potentiometer which comprises a slider in contact with a resistance track and with a conductive band, a device for controlling the displacement of the slider, and an external protective casing fitted with a detachable cover. The potentiometer comprises a lead-screw which can be operated from the exterior of the casing, a sliding unit through which the lead-screw passes and which comprises a slider applied against the resistor and a rider placed on the side opposite to the slider and slidingly applied against the casing. The sliding unit further comprises resilient arms engaged with the lead-screw and intended to drive the moving system as thus constituted. The actuating device thus permits accurate displacement of the slider and stopping of this latter at the end of travel while preventing any damage.

United States Patent Maurice [15] 3,665,364 [4 1 May 23, 1972 s41 FINE-ADJUSTMENT POTENTIOMETER [72] inventor: Jean Maurice, Nice, France 73 A Assignee: some mmae De LElectro-Reistance,

- Nice, France 22 Filed: June 22, 1970 [21 Appl.N0.: 47,972

[30] Foreign Application Priority Data July 18, 1969 France ..6924642 [52] US. Cl. ..338/180 [51] Int. Cl ..H0lc 9/02 [58] Field ofsearch ..338/180, 181

[5 6] References Cited UNITED STATES PATENTS 3,427,546 2/1969 Peart et a1 ..338/l80 3,414,862 12/ 1 968 Ginsburg ..338/180 3,237,141 2/1966 Bourns, ..338/180 3,051,921 8/1962 Bournsetal ..338/l80 2,895,116 7/1959 Morrison ..338/l80 Primary Examiner-bewis I-l. Myers Assistant Examiner-D. A. Tone Attorney-Young & Thompson ABSTRACT A fine-adjustment potentiometer which comprises a slider in contact with a resistance track and with a conductive band, a device for controlling the displacement of the slider, and an external protective casing fitted with a detachable cover. The potentiometer comprises a lead-screw which can be operated from the exterior of the casing, a sliding unit through which the lead-screw passes and which comprises a slider applied against the resistor and a rider placed on the side opposite to the slider and slidingly applied against the casing. The sliding unit further comprises resilient arms engaged with the leadscrew and intended to drive the moving system as thus constituted. The actuating device thus permits accurate displacement of the slider and stopping of this latter at the end of travel while preventing any damage.

3 Claim, 21 Drawing Figures 4 Sheets-Sheet 1 Patented May 23, 1972 Patented May 23, 1972 4 Sheets-Sheet 3 FINE-ADJUSTMENT POTENTIOMETER This invention relates to a fine-adjustment potentiometer which is primarily intended to be employed in electronic circuitry, although other applications may be contemplated.

It is known that potentiometers in which adjustment of the movable contact or slider is carried out by means of a motionreduction device are employed more particularly in the field of electronics, for circuits .requiring accurate operation. The overall size of the reduction device is usually inscribed in the dimensions of a rectangular parallelepiped having a length of 32 mm and a cross-section of 9 X 9 mm.

These devices usually comprise a rectilineal resistance con stituted by a wire which is wound on a form or by a layer of resistance material known as a track which is deposited in the form of a film on an insulating substrate. A lead-screw which can be operated from the exterior by means of a screw-driver controls the displacement of a slider along the track.

These devices are subject to a number of drawbacks: they must necessarily comprise a screw-stopping device in order to limit the travel of the slider at the ends of the track. As a rule, rotation of the lead-screw is checked by means of a mechanical stop which is integral with the lead-screw and produces action when the slider reaches the end position.

i In practice, when the components are of very small size as is particularly the case in electronic circuitry, the stop affords low resistance to the effort-multiplying action of the leadscrew even when this latter is operated with a small screwdriver.

In order to overcome this disadvantage, it has been endeavored to replace the action of the stop by that of a release system which is intended to free the slider-actuating device from the action of the lead-screw. However, the different devices employed are either delicate or complicated. In addition, the-user cannot determine the position of the slider with any degree of certainty since there is no longer any stop for preventing rotation of the lead-screw when the slider reaches the end of the track.

The object of this invention is to over come the disadvantages referred-to above and is also intended to provide novel advantages in potentiometers of this type. In accordance with the invention, the fine-adjustment potentiometer which comprises a slider in contact with a resistance track and with a conductive band, a device for controlling the displacement of the slider, and an external protective casing'fitted with a detachable cover, is characterized in that it comprises a lead-screw which can be operated from the exterior of the casing, a sliding unitthrough which the leadscrew passes and which comprises a slider applied against the resistor and a rider placed on the side opposite to the slider and slidingly applied against the casing and that the sliding unit further comprises resilient arms engaged with the leadscrew and intended to drive the moving system as thus constituted. The actuating device thus permits accurate displacement of the slider and stopping of this latter at the end of travel while preventing any damage.

In a preferred embodiment, the sliding unit comprises two bent-back resilient arms, the opposite noses of said arms being set at opposite angles of slope and engaged between the threads of the lead-screw so as to grip said lead-screw elastically. The noses thus carry out the displacement of the entire moving system, each nose being either driving or driven in the direction of rotation of the lead-screw.

In the position of engagement over the lead-screw, the noses are preferably substantially perpendicular to planes which are tangent to the flanks of the screw-threads and the transverse edges of said noses have an angle of slope which is close to the thread angle. The bent-back arms are deflected elastically under the action of the screw-threads with which they are engaged. Contacts with the threads are thus made under the best conditions.

In one advantageous solution, the lead-screw has nonthreaded cylindrical end portions and the resilient arms of the rider are disposed relative to the screw-threads in such a manner that, at the end of the threaded portion, the nose of the driving arm moves under the action of elastic expansion and is brought to bear on the smooth end portion of the leadscrew so that said nose is thus disengaged. Any danger of damage to the apparatus as a result of forcible application against a stop is thus prevented by said disengagement.

In the same embodiment, the resilient arms of the sliding unit are disposed relative to the screw-threads in such a manner that, as the rotation of the lead-screw is continued after disengagement of the driving nose, the driven nose is moved away from the lead-screw as each screw-thread passes and falls back elastically. .onto the following screw-thread, thereby producing an audible impact. The user is thus warned that the end of travel has been reached.

The slider is preferably constituted by at least one resilient strip having a V-shaped elbow forming a ridge which is elastically applied against the track and against the band while the arms of the V are counterbraced against the slider mounting and the strip can be divided into parallel tines. A good electric contact with the track and the band is thus ensured.

One of the arms of the V is advantageously elbowed at its extremity in the direction of the slider mounting and constitutes a bearing flange which is placed within a transverse prismatic recess of said slider mounting and engaged with the slider.

In a preferred solution, the cover of the casing whose internal face carries the track and the conductive band is intended to compress the slider and the rider elastically in the closed position while the rider is counterbraced against the base of the casing.

The elements of the moving system which are thus interconnected in a simple manner as a result of elastic pressure and the oppositely facing noses of the rider which produce an elastic clamping action on the screw-threads as well as the slider bearing flange which is engaged within the prismatic recess of the slider mounting constitute devices which have zero play in the longitudinal direction. This makes it possible to produce a fine-adjustment potentiometer having high precisron.

In a first particular embodiment of the invention, the sliding unit comprises a slider mounting through which the leadscrew passes freely and on which the slider bears, and a rider which is connected to the slider mounting and placed on the side remote from the slider with respect to the lead-screw, the slider, the mounting and the rider being coupled for translational motion along the lead-screw .and the rider being adapted to carry the resilient arms which are engaged with the lead-screw.

In a second particular embodiment which tends primarily to simplify the construction as well as the assembly and to reduce the overall size, the sliding unit is constructed in one piece and has a window through which the lead-screw passes and which is inclined to the axis of this latter.

Provision is thus made for a very small number of parts which simplifies the manufacture and the casing has a small height.

In a preferred form of construction, the sliding unit is constituted by a single plate formed of a resilient metal and provided with two arms at the opposite ends thereof, one arm being intended to constitute the slider and to bear on the track and on the band while the other arm constitutes the rider and is intended to be counterbraced against the base of the casing. The manufacture of this single part is thus further simplified.

The opposite sides of the window of the sliding unit have opposite inclinations and advantageously constitute oppositelyfacing noses engaged with the lead-screw on each side of its axis.

The arms are preferably formed so that, in the position of assembly, said arms are deformed elastically and exert on the sliding unit a couple which tends to maintain the noses engaged with the lead-screw. Translation-motion control of the sliding unit is thus simplified and is carried out without any longitudinal play.

In accordance with further advantageous improvements, the head of the lead-screw which is formed of insulating material is added to said conducting lead-screw and that portion of the screw which is remote from the head is journalled in a bearing which is fitted on the casing.

The conductive band which -is provided for the slider is formed of metal foil to which the corresponding external connector-pin is attached.

An insulating plate which completes the cover of the casing externally is maintained within its housing by wedging in position and secures the different elements of the potentiometer.

The foregoing improvements make it possible to simplify the assembly of the apparatus.

Further properties of the invention will become apparent from the description which follows below.

In the accompanying drawings which are given by way of example and not in any limiting sense, there is shown a preferred embodiment of the invention in an application which is intended for use in electronic circuitry. FIGS. 1 to 6 illustrate the potentiometer components which are separated from each other and superposed in their positions of assembly. These components are respectively as follows:

FIG. 1 :the casing FIG. 2 f the rider FIG. 3: the lead-screw FIG. ,4 the slider mounting FIG. 5 the slider FIG. 6 the cover.

FIG. 7 is a sectional view taken along line VII-VII of FIG. 8 and showing the assembled potentiometer.

FIG. 8 is a sectional view taken along line VIIl-VIII of FIG. 7.

FIG. 9 is a view of the inside of the cover.

FIGS. 10, 11 and 12 are respectively a bottom view, a longitudinal view and a transverse view of the rider.

FIGS. 13 and 14 are enlarged fragmentary views in sectional elevation corresponding to FIG. 7 and showing the rider respectively in the position in which it is engaged with the lead screw and in which it is located at the end of travel.

FIG. 15 is a view in perspective showing an assembled potentiometer, the casing having been partly broken away.

FIG. 16 is a longitudinal sectional view of the assembled potentiometer, this view being taken along line XVI-XVI of FIG. 19.

FIG. 17 is a sectional view taken along line XVII-XVII of FIG. 16.

F I6. 18 is a top view of the cover which has been removed.

FIG. 19 is a sectional view taken along line XIX-XIX of FIG. 16.

FIG. 20 is a sectional view taken along line XX-XX of FIG. 16.

FIG. 21 is an enlarged fragmentary sectional view of one end of the lead-screw and of the casing, the sliding unit being shown at the end of travel.

' In the example which is described with reference to FIGS. 1 to 9, the potentiometer 1 comprises a casing 2 having a para]- lelepipedal configuration, one longitudinal face of which is closed by a removable cover 3. There are mounted within the interior of the casing 2 a sliding unit and a lead-screw 5 which is passed through the unit for displacing this latter in translational motion. The sliding unit comprises a rider 4, a slider mounting 6 and a slider 7. For the sake of clarity of the description, these elements are described in the order of FIGS. 1 to 6.

The casing 2 which is formed of insulating material is pierced by bores 8 and 9 in which the extremities of the leadscrew 5 are rotatably mounted as will be described hereinafter;' the borev 8 has a diameter which is slightly larger than that of the lead screw 5 in order to permit assembly of this latter.

The rider'4"(shown in FIG. 2 and in FIGS. 10 to 12) has a base 10 which terminates in two resilient arms 11a, 11b, the

free extremities of said arms being bent back and the opposite noses l2 and 13 of which have opposite angles of inclination.

The rider 4 has two lateral lugs 14 and 15 of unequal length which are intended to ensure displacement of the slider mounting 6 as will be described later.

The lead-screw 5 consists of a body which is provided with screw-threads 16 and a joumal-surface 17 at each extremity. The diameter of the journals 1? is slightly smaller than that of the roots of the screw-threads l6.

The lead-screw 5 is rotatably mounted within the bores 8 and 9 of the casing 2 on bearings 18 and 19.

The head 21 of the lead-screw 5 is provided with a slot 22 for receiving the end of a screw-driver for the purpose of rotating said lead-screw.

A flexible annular seal 23 is interposed between the head 21 of the lead-screw and its housing and the screw is retained by means of a split washer 24.

In the operating position, the opposite noses l2 and 13 are each engaged between two consecutive threads 16 and grip the lead-screw 5 elastically (as shown in FIGS. 7 and 13).

In this same position, the nosesl2 and 13 are substantially perpendicular to the planes which are tangent to the flanks of the threads 16. By way of example, the noses portions make an angle in the vicinity of 30 with the axis of the lead-screw in the case of triangular threads having an angle of 60 at the crests.

The transverse edges of the noses 12,13 are disposed slantwise; the angle of inclination of said edges is close to that of the threads 16 and'results from the pitch and diameter of the lead-screw.

The elastic pressure exerted by the arms 11a, 11b and the noses l2, 13 on the lead-screw 5 is so determined that said noses are engaged in the threads 16 without causing abnormal deflection of the lead-screw 5. y

In the position of assembly, the noses l2, 13 are brought elastically towards the base 10 of .the rider 4 by means of the screw-threads 16 with which they are engaged. Said noses take up positions such as 12a, 13a (as shown in FIG. 13).

By rotating the lead-screw 5, the noses Hand 13 are displaced longitudinally either on one side of the lead-screw 5 or on the other, depending on the direction of rotation.

At the extremities of the lead-screwS (FIG. 14), each nose 13 or 14 moves away from the screw-threads 16'and is applied as a result of elastic expansion against the corresponding journal surface 17 in a position such as 13b.

The slider mounting 6 (shown in FIGS. 4 and 8) which is formed of insulating material and has an approximately parallelepipedal volume is cut so as to form a longitudinal channel 25 through which the lead-screwS- passes freely. Said slider mounting is provided on each transverse face with a groove 26 in which one of the lugs 14, 15 of the rider 4 is engaged without transverse play. The lugs 14, 15 are capable of sliding within the grooves 26 in a direction at right angles to the cover 3 The slider mounting 6 is also provided with a prismatic transverse notch 27 which is intended to displace the slider 7 as will be explained hereinafter.

On the face which is remote from the rider 4, said slider mounting is additionally provided with a longitudinal rib 28 on each side of which are located two longitudinal cups 29, 31 of unequal width for the purpose of guiding the slider 7.

As shown in FIGS. 5 and 7, the slider 7 is constituted by a resilient conductive strip having a V-shaped elbowed portion and elastically applied in the position of assembly against the internal face of the cover 3 by means of its ridge 32.

One of the arms of the V is elbowed at its extremity in the direction of the prismatic notch 27 so as to constitute a bearing flange 33 which is applied along the bottom of said notch in order to displace the slider 7.

The V-shaped strip issubdivided by means of longitudinal slits into a plurality of similar V-shaped tines disposed in two sets 34 and 35 between, which is formed a space 36. By way of example, the set 34 has two tines and the set 35 has three tines. The two sets of tines 34, 35 are joined together by means of the flange 33.

In theposition of assembly, the sets 34 and 35 are applied elastically against the respective edges of the cups 29, 31 (as shown in FIGS. 4 and 5) andthe rib 28 is located within the space 36.

The cover 3 is constituted by a plate of insulating material,

the contour of which seals off the cavity of the casing 2. I A conductive strip or band 37 and an electric resistance track 38 are disposed lengthwise along the internal face of the cover 3, said band and said track being parallel to each other and separated by an insulating space 39.

The set of tines 34 comes into contact through the ridge 32 with the band 37 and the set 35 comes into contact with the track 38. The respective widths of the band 37 and of the track'38 are greater than the respective widths of the sets 34 and 35 and the latter are spaced at a distance such that they bear respectively only on the band 37 or the track 38.

As shown in FIG. 7, the band 37' is connected to a terminal 41 and each extremity of the track 38 is connected to a terminal 42, 43 by means of conductors respectively designated by the references 44, 45 and 46.

The potentiometer 1 is completed by an insulating plate 47 which is attached to the cover 3 and fitted with plug connectors 48, 49 and 51 which are placed respectively opposite to the terminals 41, 42, 43.

In the position of closure, the cover 3 compresses elastically the 'V-shaped slider 7, the slider mounting 6 and the rider 4. Said rider is counter-braced against the base of the casing 2 and the slider mounting 6 is applied against the base 10.

The operation and advantages of the potentiometer as thus designedand arranged are as follows By operating the lead-screw 5 by means of a screw-driver, for example, the noses l2 and 13 which grip the screw-threads 16 elastically are either driving or driven in the direction of rotation of said lead-screw. The rider 4 thus moves longitudinally either in one direction or in the other and displaces the slider mounting-6 by means of the lugs 14, 15 which are engaged in the grooves 26.

Since the noses 12, 13 are substantially perpendicular to the planes which are tangent to the flanks of the screw-threads l6 and since their transverse edges have an obliquity which practically corresponds to the angle of the screw-threads 16, said noses can readily slide over the threads 16 and do not tend to move away from theselatter during rotation of the lead-screw 5.

The drivingmotion is carried out without any longitudinal play as a result of resilient clamping of the lead-screw 5 by means of the noses 12', 13. During the movements of translation, the rider 4remains applied against the base of the casing 2 without any possibility of pivotal movement. Compensation for any surface irregularities of the lead-screw 5 is provided by virtue of the resiliency of the arms 11a, 11b and of the noses 12, 13. The fact that the lugs 14, 15 are slidably mounted in the grooves 26 permits relative displacements of the slider mounting 6 with respect to the rider 4 at the time of assembly.

The flange 33 which is gripped between the prismatic faces of the notch 27 displaces the slider 7 without any longitudinal play.

The slider mounting 6 and the rider 4 are maintained in position by virtue of the fact that the slider 7 is applied elastically against the internal face of the cover 3.

The tines of the sets 34, 35 which are applied respectively against the central portion of the band 37 and of the track 38 provide electric contacts without any danger of disturbance. Said tines are, guided by the rib 28 and the edges of the cups 29, 31 which prevent any lateral displacement.

If rotation of the lead-screw is continued in the same direction after the driving nose such as the nose 13, for example, has passed beyond the threaded portion of the lead'screw 5 and is disengaged in position13b (as shown in FIG. 14), the driven nose 12 can still continue the movement of translation of the rider 4 as a result of its resilient pressure on the thread 16 which is located externally with respect to said nose.

But if the rotation continues and a resistance is set up, the nose 12 is moved away from the lead-screw 5 as each thread passes and moves from position 12a to position 12b (as shown in FIG. 14). The nose then falls back elastically onto the following screw-thread, thus producing an audible impact which can be likened to a click. The user is then warned that the end of travel has been reached.

The very slight movement of translation is limited by a stop (not shown) or more simply by the transverse wall 52 of the casing 2 (as shown in FIG. 14).

No damage is liable to occur since the thrust cannot be multiplied under the action of the lead-screw.

If the operator rotates the lead-screw 5 in the opposite direction, the nose l2 assumes the driving function while the nose 13 re-engages between the first threads of the lead-screw 5 and the rider moves in the opposite direction. The same cycle takes place at the other end of the lead screw 5 in the case of the nose 12.

The noses l2, 13 which produce a resilient gripping action on the threads 16 of the lead-screw 5 and the flange 33 of the slider 7 which is engaged between the convergent faces of the notch 27 of the slider mounting 6 constitute devices which have zero play in the longitudinal direction.

The potentiometer 1 which can readily be actuated from the exterior thus makes it possible to ensurethat the slider is effectively applied against the track and against the band, is displaced in a uniform manner, is disengaged at the ends of travel. It also provides an audible warning of disengagements, and a limitation at the end of travel without any danger of damage while longitudinal play is eliminated, thereby constituting a fine-adjustment potentiometer. It is readily apparent that the invention is not limited to the example hereinabove described and extends to alternative forms of execution.

Accordingly, it follows that the conductive-band 37 can be disposed on one of the lateral faces of the casing 2 instead of the internal face of the cover 3. In that case, the contact is established by means of small lateral strips or tines of the slider.

The conductive band 37 can also be disposed on a surface which is parallel to the plane of the cover 3 but located inside the casing 2 with respect to the cover.

Attachment of the slider 7 to the mounting 6 can be carried out by means of screws or rivets or alternatively by bonding.

A connection between the slider mounting 6 and the rider 4 can also be made by means of screws, rivets or by bonding.

In the example which is described with reference to FIGS. 15 to 21, the potentiometer 1 comprises, as in the previous embodiment, a casing 2 having a parallelepipedal contour, one longitudinal face of which is closed by a detachable cover 3. There is mounted within the interior of the casing 2 an annular sliding member 61 which will be described hereinafter for the sake of clarity of the description.

The casing 2 is provided at the end corresponding to the head 62 of the lead-screw 5 with a bore 8 having a diameter which is slightly greater than the maximum diameter of the lead-screw 5 in order that this latter may be fitted in position. At the opposite end, a bearing 63 in which is formed a bore 9 is mounted separately within the casing 2.

The lead-screw 5 has a structure which is similar to the previous embodiment but comprises a head 62 formed of insulating material, said head being added and forcibly fitted over the extremity of the lead-screw 5 at the time of assembly.

The lead-screw 5 is rotatably mounted at one extremity within the bore 9 of the bearing 63 and at the other extremity within the hole of a seal 64 which is fitted within an annular recess 65 which is formed in the casing 2 and is open to the exterior.

A resilient washer 66 which is fitted between the internal wallof the casing 2 and a boss 67 of the lead-screw 5 serves to maintain this latter in position.

The cover 3 is provided on the side facing the lead-screw 5 with a conductive strip or band 37 and an electric resistance track 38. The band 37 is formed of metal foil. Said band 37 is attached to the external connector-pin 48 by means of a connector 68 which passes round one edge of the cover 3. The track 38 is connected to the current-supply pins 49 and 51 by means of the end-connectors 69, 70 which are connected electrically to the-extremities of said track by application of pressure or by welding. Each connector-pin forms one piece with the corresponding end-connector.

The sliding member 61 is provided with a window 71 through which the lead-screw passes and which is inclined to the axis of this latter. Said sliding member is constituted by a single plate formed of a resilient metal such as spring steel.

The sliding member 61 is provided at the two opposite extremities thereof with'two curved arms which are shaped at the time of assembly and constitute in one case the slider 72 and in the other case the rider 73.

The arm which constitutes the slider 72 is elbowed in the direction opposite to the direction of slope of the sliding member 61 and has a return portion between the lead-screw 5 and the cover 3 in order to reduce space requirements in the longitudinal direction.

The slider 72 is provided with two terminal lugs 74a and 74b, the first lug being applied against the conductive band 37 and the second lug being applied against the resistance track 38.

The arm which constitutes the rider 73 is counterbraced against the base of the casing 2.

The window 71 has a trapezoidal contour, the convergent sides 75 of said window being located opposite to the base the casing 2 in one case and opposite to the cover 3 in the other case.

The angle of inclination of the window 71 with respect to the axisof the lead-screw 5 andthe angle of convergence of the sides .75 of said window correspond to the pitch and the thread form of the lead-screw 5 so that the sides 75 accordingly constitute oppositely facing noses of opposite inclination with respect to the threads of the lead-screw 5. Said sides are in resilient engagement with said threads on each side of the axis of the lead-screw 5.

In the position of assembly, the slider 72 and the rider 73 are deformed elastically and exert on the sliding member 61 a couple which tends to maintain the sides 75 engaged with the lead-screwS.

The potentiometer 1 is completed by an insulating plate 76 which is placed externally over the cover 3 and fitted within the cavity of the casing 2. The'plate 76 is fabricated from an insulating and rigid material which can be maintained in position by wedging and may consist, for example, of plastic material which is reinforced with glass.

The connector-pins 48, 49 and 51 pass through the plate 76 and this latter is fixed within its recess by wedging at the time of assembly.

The plate 76 is provided at the time of assembly with an outer coating of insulating sealing material 77.

Assembly of the potentiometer 1 is carried out as follows Thesliding member 61 is placed within the casing and the lead-screw 5 is inserted through the bore 8 of the casing 2. The lead-screw 5 is passed through the window 71 and the extremity of said screw is fitted in position within the bore 9 of the bearing 63. The resilient washer 66 is placed in position through the interior of the casing 2.

The cover 3 provided with the connections 68, 69, 70 and connector-pins 48, 49 and 51 is then placed in position. Finally, the plate 76 is placed within its housing and secured by wedging within this latter. Said plate serves to secure the different elements of the potentiometer in the position of assembly.

The seal 64 and the screw head 62 are the last elements to be placed in position after heat treatment of the sealing material 77 as will be explained below.

The operation of the potentiometer is identical with that of the first embodiment and has novel advantages as well as those which were already provided.

In the position of assembly, the slider 72 and the rider 73 maintain elastically the sides 75 of the window'71 (which correspond to the noses contemplated in the first embodiment), said sides being engaged with the threads of the lead-screw 5.

The sliding member 61 is displaced by rotating the lead screw 5 by means of a screw-driver, for example. The movement can be carried out in both directions.

lf rotation of the lead-screw is continued in the same direction (FIG. 2 the side 75 which constitutes the driving nose moves away from the screw thread at the end of travel and bears on the journal surface 17. The other side 75 which constitutes the driven nose continues to .be thrust forward by the corresponding screw thread until the elbow of the slider 72 comes into abutment with the wall of the casing 2. If rotation of the lead-screw 5 is continued, the driven side 75 is lifted by the thread and the sliding member comes into position 61a (as shown in the figure in chain-dotted lines) as a result of elastic deformation. The driven side 75 then passes out of the screw thread and returns to the initial position on the following thread, thereby producing an audible shock which can be compared with a click. The user is thus warned that the end of travel has been reached.

By rotating the lead-screw 5 in the opposite'direction, the sliding member 61 moves in the other direction until the side 75 which has become the driving side leaves the thread. The rider 73 comes into abutment with the wall of the casing 2 and the other side 75 which is driven produces audible impacts, and so on in sequence.

There is no danger of damage at the ends of travel since the driving nose is then disengaged.

Motion transmission is carried out without any longitudinal play as a result of reilient clamping of the lead-screw 5 by the sides 75 of the window 71. Compensation for any surface irregularities of the lead-screw 5 is ensured as a result of elastic deformations of said sides.

The potentiometer as'thus constructed provides a number of different novel advantages.

The mounting, the slider and the rider are combined in a single unit. Said unit is constituted by a cut-out, elbowed plate and is both simple and inexpensive to produce.

The elbow of the slider 72 reduces the overall longitudinal dimensions of the casing 2.

The assembly is simplified by reason of the fact that both the lead-screw 5 and the sliding member 61 can be assembled at the same time and that the added head 62 can be placed over the seal 64. No difficulty is involved in placing the leadscrew 5 in contact with the slider 72 since the screw head 62 is formed of insulating material.

Moreover, during the heat treatment which is necessary in order to harden the sealing material 77 of the plate 76 the excess air contained within the casing 2 can escape between the bore 8 and the lead-screw 5 between which a clearance is provided, the seal 64 and the head 62 being placed in position only after said treatment has been completed. This accordingly prevents any defects in leaktightness such as holes, bubbles or discharges which can be caused by pressure or reduced pressure of the air contained within a hermetically sealed casing 2.

Molding of the casing 2 is simplified inasmuch as the journal 17 is fitted within the added bearing 63.

The assembly is also simplified by reason of the fact that the connector-pins 49, 51 form one piece with their end-connectors and the connector-pin 48 is attached to its connector 68 and to the conductive band 37.

Electrical contact is improved between the lug 74a of the slider 72 and the strip or band 37 which is formed of metal foil.

The assembly is simplified to a considerable extent by virtue of the fact that the plate 76 is attached by wedging in position and that said plate secures the different elements of the potentiometer l. 7

As is readily apparent, the lugs 74a, 74b of the slider 72 can each comprise a plurality of parallel tines in order to improve the electric contacts with the band 37 and with the track 38.

lclaim:

1. A fine-adjustment potentiometer comprising an external protective casing having a detachable cover, an electrically resistive track and a conductive band parallel to said track and attached to said cover, a lead-screw supported by said casing and having a head operable from the exterior of the casing, a sliding unit coupled with the lead-screw for translational motion and comprising a slider bearing simultaneously against the resistive track and against the conductive band, a slider mounting having a recess through which the lead-screw passes freely, a rider on the side of the lead-screw opposite tothe slider and bearing against the casing, said rider comprising two resilient arms engaging the threads of the lead-screw and being elastically deflected and obliquely disposed with respect to the axis of the lead-screw in a direction substantially perpendicular to the planes tangent to the flanks of the screw threads, said rider having lugs disposed transversely to said screw and engaging recesses of the slider mounting for driving said mounting in a direction parallel to the axis of said screw while permitting a relative displacement between the rider and the slider mounting in a direction at right angles to the resistive track and the conductive band, said lead-screw having at its two end portions a smooth part the diameter of which is smaller than that of its threaded part.

2. Potentiometer according to'claim 1, wherein the transverse edges of the rider arms have an angle of slope close to the screw threads angle.

3. Potentiometer according to claim 1, wherein the slider comprises a resilient V-shaped strip divided into two sets of tines having their ridges bearing against the resistive track and the conductive band respectively, one of the arms of the V of the slider being elbowed at its end portion in the direction of the slider mounting and constituting a bearing flange which is disposed within a transverse prismatic recess of said slider mounting, and the slider mounting having a longitudinal rib disposed between said two sets of tines.

UNITED STATES PATENT OFFICE. CERTIFICATE OF CORRECTION 3,665,364 Dated May 23 1972 Patent No.

Invent0r( a Maurice It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

t 7 On the cover page [73] the name of the assignee should read SOCIETE FRANCAISE DE L'ELECTRO-RESISTANCE Signed and sealed this 7th day of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting; Officer ROBERT GOITSCHALK Commissioner of Patents FORM PC4050 (169) uscoMM-Dc 60376-P59 A .5. GOVERNMENT PRINTING OFFICE: 1969 0*365-334,

UNITED STATES PATENT OFFICE. CERTIFICATE OF CORRECTION 3,665,364 Dated Ma 23, 1972 Patent No.

Inventor s) Jean urice It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover page [73] the name of the assignee should read SOCIETE FRANCAISE DE L'ELECTRO-RESISTANCE I Signed and sealed this 7th day of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting; Officer 1 Commissioner of Patents FORM USCOMM-DC suave-ps9 U.S GOVERNMENT PRINTING OFFICE 1569 O365'334. 

1. A fine-adjustment potentiometer comprising an external protective casing having a detachable cover, an electrically resistive track and a conductive band parallel to said track and attached to said cover, a lead-screw supported by said casing and having a head operable from the exterior of the casing, a sliding unit coupled with the lead-screw for translational motion and comprising a slider bearing simultaneously against the resistive track and against the conductive band, a slider mounting having a recess through which the lead-screw passes freely, a rider on the side of the lead-screw opposite to the slider and bearing against the casing, said rider comprising two resilient arms engaging the threads of the lead-screw and being elastically deflected and obliquely disposed with respect to the axis of the lead-screw in a direction substantially perpendicular to the planes tangent to the flanks of the screw threads, said rider having lugs disposed transversely to said screw and engaging recesses of the slider mounting for driving said mounting in a direction parallel to the axis of said screw while permitting a relative displacement between the rider and the slider mounting in a direction at right angles to the resistive track and the conductive band, said leadscrew having at its two end portions a smooth part the diameter of which is smaller than that of its threaded part.
 2. Potentiometer according to claim 1, wherein the transverse edges of the rider arms have an angle of slope close to the screw threads angle.
 3. Potentiometer according to claim 1, wherein the slider comprises a resilient V-shaped strip divided into two sets of tines having their ridges bearing against the resistive track and the conductive band respectively, one of the arms of the V of the slider being elbowed at its end portion in the direction of the slider mounting and constituting a bearing flange which is disposed within a transverse prismatic recess of said slider mounting, and the slider mounting hAving a longitudinal rib disposed between said two sets of tines. 